In response to demands in the market, there have been proposed many technologies which allow a vehicle to urgently travel (travel in a runflat mode) several hundred kilometers even when the pneumatic tire is punctured while running; in recent years, safety tires and tire/wheel assemblies in which such technologies were put into practical use are gradually prevailing. Even when the inner pressure of the safety tires or tire/wheel assemblies decreases due to, for example, puncturing, it is not easy to find the decrease in the tire inner pressure apparently; therefore, the safety tires and tire/wheel assemblies are required to be used in conjunction with an apparatus for monitoring the tire condition because of assuring safety thereof.
As a conventional apparatus for monitoring the condition of a tire, Japanese Patent Application Publication No. 6-211012, for example, discloses a tire condition monitoring apparatus having an air pressure detecting means for detecting the air pressure of a tire, a temperature detecting means for detecting the temperature of a tire, and a burst generation prediction means for predicting the generation of burst of a tire based on the air pressure detected by the air pressure detecting means and the tire temperature detected by the temperature detecting means. Japanese Patent Application Publication No. 2000-355203 discloses a tire air pressure warning apparatus that detects the air pressure of a tire with a pressure sensor to inform the vehicle side of it by radio.
The above-described apparatuses can suitably be used as apparatuses for monitoring the condition of a normal pneumatic tire mounted on a vehicle; however, when the above apparatuses are used for the foregoing safety tires or tire/wheel assemblies, they can not give the driver a warning against the limit of runflat operation (the limit where the operation is stopped before the breakdown of the tire) with high accuracy during runflat operation.